Dendritic microstructure endows high-temperature strength retention without sacrificing room-temperature deformability in a V-Nb-Mo-Ta-W quinary BCC high-entropy alloy

The deformation behavior of a 5V-17Nb-19Mo-34Ta-25W high-entropy alloy (HEA) with the body-centered cubic (BCC) structure exhibiting dendritic and equiaxed microstructures with a similar grain size (∼80 μm) has been investigated in compression in a temperature range from 298 to 1773 K and in tension at room temperature. The temperature dependence of yield stress for the two microstructures follows a typical trend commonly observed for conventional BCC metals and alloys; a rapid decrease at both high and low temperatures and a plateau at intermediate temperatures. The yield stresses are essentially identical with each other at low and intermediate temperatures, but at high temperatures, the yield stresses for the dendritic microstructure are much larger than those for the equiaxed microstructure with the difference in yield stress increasing with increasing temperature and decreasing strain rate. The gradual decrease in yield stress (high temperature strength retention) is concluded to be due to the dendritic microstructure with serrated grain boundaries. Rather large compression deformability (strains at failure ∼8–10 %) are obtained for both the two microstructures with identical yield stress and work-hardening. The dendritic microstructure therefore preserves the deformability/ductility and maintains the yield strength comparable to the equiaxed microstructure at room temperature, if the lattice mismatch/misfit between the dendrite arm and interdendritic region is sufficiently small. Implications is made for the future design of BCC HEAs intended for high-temperature structural applications through controlled solidification that provides serrated grain boundaries and negligibly small lattice mismatch within the dendritic microstructure for high-temperature strength retention without compromising room-temperature performance.